Laser guides have been widely used, as optical fiber components for transmitting laser beams with high energy density, for machining equipment, etc.
Incidentally, laser machining for a surface ablation process for semiconductor, etc., using a laser beam emitted through a laser guide requires that the intensities of a laser beam at the spot irradiated with the laser beam be uniform.
A conventional optical fiber including, e.g., a core having a circular cross section, and a cladding surrounding the core is configured such that the distribution of the intensities of a laser beam at the spot irradiated with the laser beam corresponds to a Gaussian distribution. Therefore, in order to obtain uniform intensities of the laser beam at such an irradiated spot, mode scrambling is required. Here, mode scrambling denotes a process for inducing the interchange of optical power between modes in an optical waveguide, e.g., by winding an optical fiber while bending the optical fiber within the range of allowable bend radii of the fiber. However, since this mode scrambling requires the winding of an optical fiber, the optical fiber may be broken, and the size of a mode scrambling device (mode scrambler) may increase. In addition, sufficiently uniform light intensities cannot be obtained by merely winding an optical fiber having a length of hundreds of meters. This decreases processing efficiency.
PATENT DOCUMENT 1 describes an optical waveguide fiber including a core material functioning to allow light to propagate and having a rectangular cross section. Furthermore, PATENT DOCUMENT 1 describes that the optical waveguide fiber functions to obtain a uniform light intensity distribution. In view of the above, it has been widely known that the use of an optical fiber including a core having a rectangular cross section allows the irradiation intensities of a laser beam at the spot irradiated with the laser beam to be uniform.    PATENT DOCUMENT 1: Japanese Examined Patent Publication No. H03-49591